The present invention relates to a new and distinct variety of Prunus persica L. Batsch white flat peach tree. This new tree, named ‘FLATPRINCESSE’, produces very long lifetime, good eating quality, semi-freestone flesh fruit for fresh market in August in the 66 —Pyrénées Orientales departement—France. Contrast is made to ‘MAILLARFLAT’ flat peach, standard varieties, for reliable description. ‘FLATPRINCESSE’ is a promising candidate for commercial success in that it has a very high regular productivity and has the same well fruit quality as other varieties: ‘MAILLARFLAT’ (unpatented), ‘FLATPRETTY’ (pending U.S. Plant Pat. application No.11/434,796), ‘FLATQUEEN’ (pending U.S. Plant Pat. application No.11/434,799) and ‘FLATNICE’ (unpatented).